Wireless communication terminal and wireless communication method for multiuser edca operation

ABSTRACT

The present invention relates to a wireless communication terminal and a wireless communication method for a multi-user EDCA operation, and more particularly, to a wireless communication terminal and a wireless communication method for performing a combination of a legacy EDCA operation and a multi-user EDCA operation. To this end, provided are a wireless communication terminal including: a communication unit; and a processor configured to control transmission and reception of a wireless signal through the communication unit, wherein the processor updates enhanced distributed channel access (EDCA) parameters for channel access, the EDCA parameters being updated based on an EDCA parameter set selected from a first EDCA parameter set and a second EDCA parameter set, and performs channel access based on the updated EDCA parameters and a wireless communication method using the same.

TECHNICAL FIELD

The present invention relates to a wireless communication terminal and awireless communication method for a multi-user EDCA operation, and moreparticularly, to a wireless communication terminal and a wirelesscommunication method for performing a combination of a legacy EDCAoperation and a multi-user EDCA operation.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelessLAN technology that can provide a rapid wireless Internet service to themobile apparatuses has been significantly spotlighted. The wireless LANtechnology allows mobile apparatuses including a smart phone, a smartpad, a laptop computer, a portable multimedia player, an embeddedapparatus, and the like to wirelessly access the Internet in home or acompany or a specific service providing area based on a wirelesscommunication technology in a short range.

Institute of Electrical and Electronics Engineers (IEEE) 802.11 hascommercialized or developed various technological standards since aninitial wireless LAN technology is supported using frequencies of 2.4GHz. First, the IEEE 802.11b supports a communication speed of a maximumof 11 Mbps while using frequencies of a 2.4 GHz band. IEEE 802.11a whichis commercialized after the IEEE 802.11b uses frequencies of not the 2.4GHz band but a 5 GHz band to reduce an influence by interference ascompared with the frequencies of the 2.4 GHz band which aresignificantly congested and improves the communication speed up to amaximum of 54 Mbps by using an OFDM technology. However, the IEEE802.11a has a disadvantage in that a communication distance is shorterthan the IEEE 802.11b. In addition, IEEE 802.11g uses the frequencies ofthe 2.4 GHz band similarly to the IEEE 802.11b to implement thecommunication speed of a maximum of 54 Mbps and satisfies backwardcompatibility to significantly come into the spotlight and further, issuperior to the IEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of awireless interface accepted by 802.11n, such as a wider wirelessfrequency bandwidth (a maximum of 160 MHz), more MIMO spatial streams (amaximum of 8), multi-user MIMO, and high-density modulation (a maximumof 256 QAM). Further, as a scheme that transmits data by using a 60 GHzband instead of the existing 2.4 GHz/5 GHz, IEEE 802.11ad has beenprovided. The IEEE 802.11ad is a transmission standard that provides aspeed of a maximum of 7 Gbps by using a beamforming technology and issuitable for high bit rate moving picture streaming such as massive dataor non-compression HD video. However, since it is difficult for the 60GHz frequency band to pass through an obstacle, it is disadvantageous inthat the 60 GHz frequency band can be used only among devices in ashort-distance space.

Meanwhile, in recent years, as next-generation wireless LAN standardsafter the 802.11ac and 802.11ad, discussion for providing ahigh-efficiency and high-performance wireless LAN communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless LAN environment, communication havinghigh frequency efficiency needs to be provided indoors/outdoors underthe presence of high-density stations and access points (APs) andvarious technologies for implementing the communication are required.

DISCLOSURE Technical Problem

The present invention has an object to providehigh-efficiency/high-performance wireless LAN communication in ahigh-density environment as described above.

In addition, the present invention has an object to manage and controlparameters for a multi-user EDCA operation in addition to a legacy EDCAoperation.

Technical Solution

In order to achieve the objects, the present invention provides awireless communication method and a wireless communication terminal asbelow.

First, an exemplary embodiment of the present invention provides awireless communication terminal, including: a communication unit; and aprocessor configured to control transmission and reception of a wirelesssignal through the communication unit, wherein the processor is updatesenhanced distributed channel access (EDCA) parameters for channelaccess, the EDCA parameters being updated based on an EDCA parameter setselected from a first EDCA parameter set and a second EDCA parameterset, and performs channel access based on the updated EDCA parameters.

In this case, the second EDCA parameter set may be a multi-user (MU)EDCA parameter set, and when the EDCA parameters are updated based onthe MU EDCA parameter set, the processor may set an MU EDCA timerindicating a duration of performing channel access using parametersupdated based on the MU EDCA parameter set.

According to an embodiment of the present invention, when the terminaldoes not participate in an uplink multi-user (UL-MU) transmission, theprocessor may transmit a frame containing an operating mode indication(OMI) information in which a UL-MU disable subfield indicates asuspension of a UL-MU operation, and when an immediate acknowledgmentfor the frame containing the OMI information is received from an OMIresponder, the processor may set the MU EDCA timer to zero.

Further, when the immediate acknowledgment for the frame containing theOMI information is received from the OMI responder, the processor mayset MU EDCA timers of all access categories to zero.

According to an embodiment, when the MU EDCA timer reaches zero, theprocessor may update the EDCA parameters based on the first EDCAparameter set most recently received from a base wireless communicationterminal to which the terminal is associated.

According to another embodiment, when the MU EDCA timer reaches zero,the processor may update the EDCA parameters based on a predetermineddefault EDCA parameter set if the first EDCA parameter set has not beenreceived from a base wireless communication terminal to which theterminal is associated.

Further, the MU EDCA timer may be set to a value of an MU EDCA timersubfield of the MU EDCA parameter set most recently received from a basewireless communication terminal to which the terminal is associated.

Further, at least one parameter of the second EDCA parameter set mayhave a value greater than a corresponding parameter of the first EDCAparameter set.

Further, the channel access may be performed based on a backoffprocedure using a backoff timer obtained within a contention window of acorresponding access category, and the EDCA parameters may include acontention window minimum value and a contention window maximum valuefor setting the contention window.

Further, the first EDCA parameter set and the second EDCA parameter setmay be received via at least one of a beacon, a probe response, and anassociation response transmitted by a base wireless communicationterminal to which the terminal is associated.

In addition, another exemplary embodiment of the present inventionprovides a wireless communication method of a wireless communicationterminal, including: updating enhanced distributed channel access (EDCA)parameters for channel access, wherein the EDCA parameters are updatedbased on an EDCA parameter set selected from a first EDCA parameter setand a second EDCA parameter set; and performing channel access based onthe updated EDCA parameters.

In this case, the second EDCA parameter set may be a multi-user (MU)EDCA parameter set, and when the EDCA parameters are updated based onthe MU EDCA parameter set, the method further includes: setting an MUEDCA timer indicating a duration of performing channel access usingparameters updated based on the MU EDCA parameter set.

According to an embodiment of the present invention, when the terminaldoes not participate in an uplink multi-user (UL-MU) transmission, themethod further includes: transmitting a frame containing an operatingmode indication (OMI) information in which a UL-MU disable subfieldindicates a suspension of a UL-MU operation, and when an immediateacknowledgment for the frame containing the OMI information is receivedfrom an OMI responder, the method further includes: setting the MU EDCAtimer to zero.

Further, when the immediate acknowledgment for the frame containing theOMI information is received from the OMI responder, the setting the MUEDCA timer to zero includes setting MU EDCA timers of all accesscategories to zero.

According to an embodiment, when the MU EDCA timer reaches zero, theupdating step includes updating the EDCA parameters based on the firstEDCA parameter set most recently received from a base wirelesscommunication terminal to which the terminal is associated.

According to another embodiment, when the MU EDCA timer reaches zero,the updating step includes updating the EDCA parameters based on apredetermined default EDCA parameter set if the first EDCA parameter sethas not been received from a base wireless communication terminal towhich the terminal is associated.

Further, the MU EDCA timer may be set to a value of an MU EDCA timersubfield of the MU EDCA parameter set most recently received from a basewireless communication terminal to which the terminal is associated.

Further, at least one parameter of the second EDCA parameter set has avalue greater than a corresponding parameter of the first EDCA parameterset.

Further, the channel access may be performed based on a backoffprocedure using a backoff timer obtained within a contention window of acorresponding access category, and the EDCA parameters may include acontention window minimum value and a contention window maximum valuefor setting the contention window.

Further, the first EDCA parameter set and the second EDCA parameter setmay be received via at least one of a beacon, a probe response, and anassociation response transmitted by a base wireless communicationterminal to which the terminal is associated.

Advantageous Effects

According to an embodiment of the present invention, switching betweenthe legacy EDCA operation and the multi-user EDCA operation can beefficiently managed.

According to an embodiment of the present invention, it is possible toincrease the total resource utilization rate in the contention-basedchannel access system and improve the performance of the wireless LANsystem.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a wireless LAN system according to an embodiment ofthe present invention.

FIG. 2 illustrates a wireless LAN system according to another embodimentof the present invention.

FIG. 3 illustrates a configuration of a station according to anembodiment of the present invention.

FIG. 4 illustrates a configuration of an access point according to anembodiment of the present invention.

FIG. 5 schematically illustrates a process in which a STA and an AP seta link.

FIG. 6 illustrates a carrier sense multiple access (CSMA)/collisionavoidance (CA) method used in wireless LAN communication.

FIG. 7 illustrates a switching operation between a legacy EDCA mode anda multi-user EDCA mode according to an embodiment of the presentinvention.

FIG. 8 illustrates a configuration of a multi-user EDCA parameter setelement according to an embodiment of the present invention.

FIG. 9 illustrates a method of transmitting a multi-user EDCA parameterset according to an embodiment of the present invention.

FIG. 10 illustrates a method of disabling a multi-user EDCA according toan embodiment of the present invention.

FIG. 11 illustrates a configuration of an operating mode indicationelement according to an embodiment of the present invention.

FIG. 12 illustrates a method of controlling multi-user transmissionaccording to operating mode indication information.

FIG. 13 illustrates a method for disabling a multi-user EDCA accordingto another embodiment of the present invention.

FIG. 14 illustrates a method for disabling a multi-user EDCA accordingto yet another embodiment of the present invention.

FIG. 15 illustrates a configuration of an HE MU PPDU according to anembodiment of the present invention.

FIG. 16 illustrates a configuration of an HE MU PPDU according toanother embodiment of the present invention.

FIG. 17 illustrates a configuration of an HE MU PPDU according to yetanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Terms used in the specification adopt general terms which are currentlywidely used by considering functions in the present invention, but theterms may be changed depending on an intention of those skilled in theart, customs, and emergence of new technology. Further, in a specificcase, there is a term arbitrarily selected by an applicant and in thiscase, a meaning thereof will be described in a corresponding descriptionpart of the invention. Accordingly, it should be revealed that a termused in the specification should be analyzed based on not just a name ofthe term but a substantial meaning of the term and contents throughoutthe specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “or more” or “or less” based on a specificthreshold may be appropriately substituted with “more than” or “lessthan”, respectively.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2016-0122488 and 10-2017-0020966 filed in the KoreanIntellectual Property Office and the embodiments and mentioned itemsdescribed in the respective application, which forms the basis of thepriority, shall be included in the Detailed Description of the presentapplication.

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention. The wireless LAN system includesone or more basic service sets (BSS) and the BSS represents a set ofapparatuses which are successfully synchronized with each other tocommunicate with each other. In general, the BSS may be classified intoan infrastructure BSS and an independent BSS (IBSS) and FIG. 1illustrates the infrastructure BSS between them.

As illustrated in FIG. 1, the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a wireless medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a non-AP STA, or an AP, or to both terms. A station forwireless communication includes a processor and a communication unit andaccording to the embodiment, may further include a user interface unitand a display unit. The processor may generate a frame to be transmittedthrough a wireless network or process a frame received through thewireless network and besides, perform various processing for controllingthe station. In addition, the communication unit is functionallyconnected with the processor and transmits and receives frames throughthe wireless network for the station. According to the presentinvention, a terminal may be used as a term which includes userequipment (UE).

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense. In the present invention, an AP may also be referredto as a base wireless communication terminal. The base wirelesscommunication terminal may be used as a term which includes an AP, abase station, an eNB (i.e. eNodeB) and a transmission point (TP) in abroad sense. In addition, the base wireless communication terminal mayinclude various types of wireless communication terminals that allocatemedium resources and perform scheduling in communication with aplurality of wireless communication terminals.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless LAN systemaccording to another embodiment of the present invention. In theembodiment of FIG. 2, duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 1, will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention. As illustrated inFIG. 3, the station 100 according to the embodiment of the presentinvention may include a processor 110, a communication unit 120, a userinterface unit 140, a display unit 150, and a memory 160.

First, the communication unit 120 transmits and receives a wirelesssignal such as a wireless LAN packet, or the like and may be embedded inthe station 100 or provided as an exterior. According to the embodiment,the communication unit 120 may include at least one communication moduleusing different frequency bands. For example, the communication unit 120may include communication modules having different frequency bands suchas 2.4 GHz, 5 GHz, and 60 GHz. According to an embodiment, the station100 may include a communication module using a frequency band of 6 GHzor more and a communication module using a frequency band of 6 GHz orless. The respective communication modules may perform wirelesscommunication with the AP or an external station according to a wirelessLAN standard of a frequency band supported by the correspondingcommunication module. The communication unit 120 may operate only onecommunication module at a time or simultaneously operate multiplecommunication modules together according to the performance andrequirements of the station 100. When the station 100 includes aplurality of communication modules, each communication module may beimplemented by independent elements or a plurality of modules may beintegrated into one chip. In an embodiment of the present invention, thecommunication unit 120 may represent a radio frequency (RF)communication module for processing an RF signal.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the communication unit120, and the like. That is, the processor 110 may be a modem or amodulator/demodulator for modulating and demodulating wireless signalstransmitted to and received from the communication unit 120. Theprocessor 110 controls various operations of wireless signaltransmission/reception of the station 100 according to the embodiment ofthe present invention. A detailed embodiment thereof will be describedbelow.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the communication unit 120 may be implemented whilebeing integrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention. As illustrated inFIG. 4, the AP 200 according to the embodiment of the present inventionmay include a processor 210, a communication unit 220, and a memory 260.In FIG. 4, among the components of the AP 200, duplicative descriptionof parts which are the same as or correspond to the components of thestation 100 of FIG. 2 will be omitted.

Referring to FIG. 4, the AP 200 according to the present inventionincludes the communication unit 220 for operating the BSS in at leastone frequency band. As described in the embodiment of FIG. 3, thecommunication unit 220 of the AP 200 may also include a plurality ofcommunication modules using different frequency bands. That is, the AP200 according to the embodiment of the present invention may include twoor more communication modules among different frequency bands, forexample, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200 mayinclude a communication module using a frequency band of 6 GHz or moreand a communication module using a frequency band of 6 GHz or less. Therespective communication modules may perform wireless communication withthe station according to a wireless LAN standard of a frequency bandsupported by the corresponding communication module. The communicationunit 220 may operate only one communication module at a time orsimultaneously operate multiple communication modules together accordingto the performance and requirements of the AP 200. In an embodiment ofthe present invention, the communication unit 220 may represent a radiofrequency (RF) communication module for processing an RF signal.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. According to an embodiment, the processor210 may be a modem or a modulator/demodulator for modulating anddemodulating wireless signals transmitted to and received from thecommunication unit 220. The processor 210 controls various operationssuch as wireless signal transmission/reception of the AP 200 accordingto the embodiment of the present invention. A detailed embodimentthereof will be described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5, the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b). In this specification, an association basically means awireless association, but the present invention is not limited thereto,and the association may include both the wireless association and awired association in a broad sense.

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5, the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

FIG. 6 illustrates a carrier sense multiple access (CSMA)/collisionavoidance (CA) method used in wireless LAN communication.

A terminal that performs a wireless LAN communication checks whether achannel is busy by performing carrier sensing before transmitting data.When a wireless signal having a predetermined strength or more issensed, it is determined that the corresponding channel is busy and theterminal delays the transmission on the corresponding channel. Such aprocess is referred to as clear channel assessment (CCA) and a level todecide whether the corresponding signal is sensed is referred to as aCCA threshold. When a wireless signal having the CCA threshold or more,which is received by the terminal, indicates the corresponding terminalas a receiver, the terminal processes the received wireless signal.Meanwhile, when a wireless signal is not sensed in the correspondingchannel or a wireless signal having a strength smaller than the CCAthreshold is sensed, it is determined that the channel is idle.

When it is determined that the channel is idle, each terminal havingdata to be transmitted performs a backoff procedure after an inter framespace (IFS) time depending on a situation of each terminal, forinstance, an arbitration IFS (AIFS), a PCF IFS (PIFS), or the likeelapses. According to the embodiment, the AIFS may be used as acomponent which substitutes for the existing DCF IFS (DIFS). Eachterminal stands by while decreasing slot time(s) as long as a randomnumber, that is, a backoff counter determined by the correspondingterminal during an interval of an idle state of the channel and aterminal that completely exhausts the slot time(s) attempts to transmiton the corresponding channel. As such, an interval in which eachterminal performs the backoff procedure is referred to as a contentionwindow interval.

When a specific terminal successfully accesses the channel, thecorresponding terminal may transmit data through the channel. However,when the terminal which attempts the transmission collides with anotherterminal, the terminals which collide with each other are assigned withnew random numbers (i.e. backoff counters), respectively to perform thebackoff procedure again. According to an embodiment, a random numbernewly assigned to each terminal may be decided within a range (2*CW)which is twice larger than a range (a contention window, CW) of a randomnumber which the corresponding terminal has previously used. Meanwhile,each terminal accesses the channel by performing the backoff procedureagain in a next contention window interval and in this case, eachterminal performs the backoff procedure from slot time(s) which remainedin the previous contention window interval. By such a method, therespective terminals that perform the wireless LAN communication mayavoid a mutual collision for a specific channel.

Multi-User Transmission

When using orthogonal frequency division multiple access (OFDMA) ormulti-input multi-output (MIMO), a wireless communication terminal cansimultaneously transmit data to one or more wireless communicationterminals. Further, one or more wireless communication terminals cansimultaneously transmit data to a wireless communication terminal. Forexample, a downlink multi-user (DL-MU) transmission in which an APsimultaneously transmits data to one or more STAs, and an uplinkmulti-user (UL-MU) transmission in which one or more STAs simultaneouslytransmit data to the AP may be performed.

In order to perform the UL-MU transmission, a resource unit to be usedby each STA and the transmission start time of each STA that performsuplink transmission should be determined. According to an embodiment ofthe present invention, the UL-MU transmission process may be managed bythe AP. The UL-MU transmission may be performed in response to a triggerframe transmitted by the AP. The trigger frame indicates a UL-MUtransmission a SIFS time after the completion of the transmission of thePHY protocol data unit (PPDU) carrying the trigger frame. Further, thetrigger frame delivers resource unit allocation information for theUL-MU transmission. When the AP transmits a trigger frame, one or moreSTAs transmit uplink data through each allocated resource unit at thetime specified by the trigger frame. A UL-MU transmission in response tothe trigger frame is performed by a trigger-based PPDU. After the uplinkdata transmission is completed, the AP transmits an ACK to STAs thathave successfully transmitted uplink data. In this case, the AP maytransmit a predetermined multi-STA block ACK (M-BA) as an ACK for one ormore STAs.

In the non-legacy wireless LAN system, a specific number, for example,26, 52, or 106 tones may be used as a resource unit for asubchannel-based access in a channel of 20 MHz band. Accordingly, thetrigger frame may indicate identification information of each STAparticipating in the UL-MU transmission and information of the allocatedresource unit. The identification information of the STA includes atleast one of an association ID (AID), a partial AID, and a MAC addressof the STA. Further, the information of the resource unit includes thesize and placement information of the resource unit.

Multi-User Enhanced Distributed Channel Access (EDCA)

A wireless communication terminal using an unlicensed band as in awireless LAN system can access a channel through a contention procedure.A terminal which has data to be transmitted does not attempt to transmitimmediately but attempts to transmit after a predetermined waiting time(e.g., AIFS[AC]) designated for each access category (AC) to which eachtraffic belongs. If the channel is switched from a busy state to an idlestate, the terminal performs a backoff procedure after the designatedwaiting time. For the backoff procedure, the terminal sets a randomnumber obtained from a contention window (i.e., CW[AC]) of thecorresponding access category to a backoff timer (or backoff counter).The terminal decrements the backoff timer while the channel is idle, andmay perform transmission when the value of the backoff timer reacheszero. Such a designated waiting time (i.e., AIFS[AC]), a contentionwindow (i.e., CW [AC]), a contention window minimum value (i.e., CWmin),a contention window maximum value (i.e., CWmax) for the channel accessmay be maintained and managed for each access category.

As described above, a UL-MU transmission can be performed in thenon-legacy wireless LAN system. The AP triggers the uplink transmissionof one or more STAs. In this case, the AP accesses the channel totrigger UL-MU transmission. On the other hand, each STA may access thechannel separately to transmit data of the corresponding STA. If a UL-MUtransmission of a STA is triggered during an individual access procedureof the corresponding STA, the STA may suspend the individual accessprocedure and perform the UL-MU transmission. Therefore, the STA has ahigh competitive advantage compared to a legacy terminal because it hasthe redundant transmission opportunity through the individualtransmission and the UL-MU transmission for the same traffic. Inaddition, since the AP and the STA simultaneously compete for traffictransmission of the specific STA, the probability of a collision mayincrease.

In order to solve such a problem, according to the embodiment of thepresent invention, a separate EDCA parameter set for a STA participatingin the UL-MU transmission can be used. The EDCA parameter set is a setof parameters for channel access, including AIFSN, CWmin and CWmax ofthe corresponding AC. The AIFSN indicates the number of slots after aSIFS included in the designated waiting time (i.e., AIFS). In theembodiment of the present invention, an EDCA parameter set used in alegacy wireless LAN system is referred to as a legacy EDCA parameter set(or a first EDCA parameter set), and a separate EDCA parameter set usedfor a STA participating in the UL-MU transmission in the non-legacywireless LAN system is referred to as a multi-user (MU) EDCA parameterset (or a second EDCA parameter set). In addition, an EDCA parameter setand EDCA parameter set element may be used as terms having the samemeaning. The legacy EDCA parameter set and the MU EDCA parameter set maybe received via at least one of a beacon, a probe response, and anassociation response transmitted by the AP to which the STA isassociated.

According to the embodiment of the present invention, at least oneparameter of the MU EDCA parameter set may have a value greater than acorresponding parameter of the legacy EDCA parameter set. For example, aCWmax value of a particular AC in the MU EDCA parameter set may be setto be greater than a CWmax value of the same AC in the legacy parameterset. In addition, an AIFSN value of a particular AC in the MU EDCAparameter set may be set to be greater than an AIFSN value of the sameAC in the legacy parameter set. By using the MU EDCA parameter setconfigured as above, the STA participating in the UL-MU transmission mayperform individual channel access with a lower transmission probabilitythan the conventional method.

FIG. 7 illustrates a switching operation between a legacy EDCA mode anda multi-user EDCA mode according to an embodiment of the presentinvention. A STA according to an embodiment of the present invention mayupdate the EDCA parameters for channel access based on an EDCA parameterset selected from the legacy EDCA parameter set and the MU EDCAparameter set. The STA performs channel access based on the updated EDCAparameters. Thus, the STA may perform switching between a legacy EDCAmode 50 a, 50 b in which channel access is performed using the legacyEDCA parameter set and an MU EDCA mode 60 in which channel access isperformed using the MU EDCA parameter set. In the embodiment of thepresent invention, switching between the legacy EDCA mode 50 a, 50 b andthe MU EDCA mode 60 may indicate a mode switching of a particular accesscategory.

Referring to FIG. 7, a STA that has succeeded in the UL-MU transmissionmay switch from the legacy EDCA mode 50 a to the MU EDCA mode 60. Morespecifically, the STA switches from the legacy EDCA mode 50 a to the MUEDCA mode 60 when the following conditions are satisfied.

First condition: The STA should receive a trigger frame 410 indicatingthe UL-MU transmission of the STA from the AP. That is, the STA shouldreceive the trigger frame 410 containing a user information fieldindicating an AID of the corresponding STA. In this case, the triggerframe may be a basic trigger frame.

Second condition: In response to receiving the trigger frame 410, theSTA should transmit a trigger-based PPDU 420 to the AP. In this case,the trigger-based PPDU 420 should contain a QoS data frame.

Third condition: The STA should receive an immediate acknowledgment 430from the AP for the trigger-based PPDU 420. In this case, the immediateacknowledgment may indicate that the recipient transmits a response tothe sender within a predetermined duration of time within the sametransmission opportunity (TXOP). An M-BA may be used as an embodiment ofthe immediate acknowledgment 430, but the present invention is notlimited thereto.

If the above three conditions are satisfied, the STA may switch the modeof the corresponding access category from the legacy EDCA mode 50 a tothe MU EDCA mode 60. When switched to the MU EDCA mode 60, the STAupdates the EDCA parameters of the corresponding access category basedon the MU EDCA parameter set. More specifically, the STA updatesAIFSN[AC], CWmin[AC] and CWmax[AC] values of all categories in which QoSdata was successfully transmitted via the trigger-based PPDU 420 withthe values specified in the MU EDCA parameter set. The STA uses theupdated EDCA parameters to access the channel. More specifically, theSTA newly sets a contention window based on the updated contentionwindow minimum value and/or contention window maximum value and obtainsa back off timer within the set contention window. The STA performs thebackoff procedure using the obtained backoff timer.

According to a further embodiment of the present invention, the firstcondition and the second condition may include a case that the STAreceives a trigger frame 410 indicating at least one random accessresource unit from the AP and transmits the trigger-based PPDU 420through a random access in response thereto. In addition, if thetrigger-based PPDU 420 transmitted by the STA does not request animmediate acknowledgment, the third condition may be omitted. In thiscase, the STA may switch from the legacy EDCA mode 50 a to the MU EDCAmode 60 when the first condition and the second condition are satisfiedregardless of whether the immediate acknowledgment 430 is received ornot.

According to an embodiment, the STA may switch to the MU EDCA mode 60 atthe time when receiving the immediate acknowledgment 430 from the AP forthe trigger-based PPDU 420. According to another embodiment, if thetrigger-based PPDU 420 transmitted by the STA does not request animmediate acknowledgment, the STA may switch to the MU EDCA mode 60 atthe time when the transmission of the trigger-based PPDU 420 iscompleted.

When the mode of the particular access category of the STA switches fromthe legacy EDCA mode 50 a to the MU EDCA mode 60, the STA sets an MUEDCA timer for the corresponding access category (i.e.,HEMUEDCATimer[AC]). The MU EDCA timer indicates a duration of performingchannel access for the corresponding access category using parametersupdated based on the MU EDCA parameter set. In this case, the MU EDCAtimer may be maintained and managed for each access category. Also, theMU EDCA timer information may be included in the MU EDCA parameter set.The MU EDCA parameter set may represent the MU EDCA timer informationvia an MU EDCA timer subfield. The STA sets the MU EDCA timer with avalue of the MU EDCA timer subfield of the MU EDCA parameter set mostrecently received from the AP to which the STA is associated.

The MU EDCA timer is decremented unless the STA succeeds in additionalUL-MU transmission. When the MU EDCA timer reaches zero, the STAswitches the mode of the corresponding access category from the MU EDCAmode 60 to the legacy EDCA mode 50 b. By setting the MU EDCA timer asabove, if additional UL-MU transmission is not successful for a certainduration of time after the MU EDCA parameter set is applied, the STA mayreturn to the legacy EDCA mode 50 b.

If the mode of the particular access category of the STA switches fromthe MU EDCA mode 60 to the legacy EDCA mode 50 b (i.e., the MU EDCAtimer of the particular access category reaches zero), the STA updatesthe EDCA parameters of the corresponding access category based on thelegacy parameter set. According to an embodiment, the STA may update theEDCA parameters based on the legacy EDCA parameter set most recentlyreceived from the AP to which the STA is associated. If the legacy EDCAparameter set is not received from the AP to which the STA isassociated, the STA updates the EDCA parameters based on thepredetermined default EDCA parameter set. The STA uses the updated EDCAparameters to access the channel. More specifically, the STA newly setsa contention window based on the updated contention window minimum valueand/or the contention window maximum value and obtains a back off timerwithin the set contention window. The STA performs the backoff procedureusing the obtained backoff timer.

FIG. 8 illustrates a configuration of a multi-user EDCA parameter setelement according to an embodiment of the present invention. Morespecifically, FIG. 8(a) illustrates the MU EDCA parameter set element,and FIG. 8(b) illustrates the abbreviated MU EDCA parameter set element.Further, FIG. 8(c) illustrates elements of the ‘MU QoS Info’ fieldincluded in the MU EDCA parameter set or the abbreviated MU EDCAparameter set.

Referring to FIG. 8(a), the MU EDCA parameter set element includeselement identifier fields, that is, an ‘Element ID’ field and an‘Element ID Extension’ field. In addition, the MU EDCA parameter setelement also includes a plurality of ‘MU AC Parameter Record’ fieldsthat represent the EDCA parameters of each access category. Morespecifically, the MU EDCA parameter set element includes a ‘MU AC_BEParameter Record’ field, a ‘MU AC_BK Parameter Record’ field, a ‘MUAC_VI Parameter Record’ field, and a ‘MU AC_VO Parameter Record’ field.Each ‘MU AC Parameter Record’ field may indicate the EDCA parameters ofthe corresponding access category, that is, AIFSN, CWmin and CWmaxvalues. Further, the MU EDCA parameter set element may also include MUEDCA timer information for each access category.

The MU EDCA parameter set element may be transmitted via a proberesponse and/or an association response in a step that the STA initiallyestablishes a link with the AP. In addition, the MU EDCA parameter setelement may be transmitted via a beacon frame while the AP is operatingthe MU EDCA parameters in the BSS. The STA receiving the MU EDCAparameter set element may update the EDCA parameters of each accesscategory based on the values of the ‘MU AC Parameter Record’ field inthe MU EDCA mode.

Meanwhile, the MU EDCA parameter set element includes an ‘MU QoS Info’field. Referring to FIG. 8(c), the ‘MU QoS Info’ field includes an ‘MUEDCA Parameter Set Update Count’ subfield (hereinafter, an update countsubfield). The update count subfield is initially set to zero and isincremented each time the MU EDCA parameter is changed. Accordingly, theupdate count subfield indicates information on how many times the MUEDCA parameter has been changed.

The AP may increment the update count subfield value by 1 when changingthe MU EDCA parameter set. The STA which has received the MU EDCAparameter set from the AP may determine whether to change the MU EDCAparameter set based on the value of the update count subfield.Meanwhile, the format of the subfields of the ‘MU QoS Info’ field otherthan the update count subfield may be the same as the format of thecorresponding subfields of the existing ‘QoS Info’ field.

FIG. 8(b) illustrates an abbreviated MU EDCA parameter set elementaccording to a further embodiment of the invention. If the value of theupdate count subfield of the MU EDCA parameter set received via thebeacon frame or the like has not been changed from the update countsubfield value previously obtained by the STA, the STA may not check thefollowing ‘MU AC Parameter Record’ field. Thus, it may be inefficient totransmit the ‘MU AC Parameter Record’ field for every beacon frame ifthe value of the update count subfield has not been changed. Therefore,as shown in FIG. 8(b), an MU EDCA parameter set in which the ‘MU ACParameter Record’ field is omitted, that is, an abbreviated MU EDCAparameter set may be used. The AP may selectively transmit the MU EDCAparameter set or the abbreviated MU EDCA parameter set based on whetheror not the value of the update count subfield is changed.

FIG. 9 illustrates a method of transmitting a multi-user EDCA parameterset according to an embodiment of the present invention. Referring toFIG. 9, an AP may transmit an MU EDCA parameter set through an initiallink setup frame 510. In this case, the initial link setup frame 510includes at least one of a probe response and an association response.In addition, the AP may transmit the MU EDCA parameter set throughperiodically transmitted beacon frames 520.

According to the embodiment of FIG. 9, the value of the update countsubfield in the initial link setup frame 510 and beacon frames 520 a,520 b is set to 5. However, the MU EDCA parameter set is changed aftertransmission of the beacon frame 520 b and the AP increments the valueof the update count subfield by 1. Thus, the value of the update countsubfield in beacon frames 520 c, 520 d, and 520 e is set to 6.

According to an embodiment of the present invention, if the value of theupdate count subfield is not changed from the previous value, the AP maytransmit the abbreviated MU EDCA parameter set via the beacon frames 520a, 520 b, 520 d and 520 e. The AP may transmit the MU EDCA parameter setthrough the beacon frame 520 c only if the value of the update countsubfield has changed from the previous value. If it is identified in thereceived beacon frame 520 c that the value of the update count subfieldhas been changed from the previously obtained update count subfieldvalue, the STA may check the ‘MU AC Parameter Record’ field to obtainthe MU EDCA parameters.

According to another embodiment of the present invention, the AP maytransmit the abbreviated MU EDCA parameter set for each beacon frame 520a, 520 b, 520 c, 520 d, and 520 e. If it is identified in the receivedbeacon frame 520 c that the value of the update count subfield ischanged from the previously obtained update count subfield value, theSTA may transmit a probe request frame or the like to request the AP totransmit the MU EDCA parameter set.

When switching to the MU EDCA mode, the STA updates the EDCA parametersbased on the MU EDCA parameter set. In this case, the STA may update theEDCA parameters based on the MU EDCA parameter set most recentlyreceived from the AP to which the STA is associated. If the MU EDCAparameter set is not received from the AP to which the STA isassociated, the STA may update the EDCA parameters based on thepredetermined default MU EDCA parameter set. If the default MU EDCAparameter set is not present, the STA may update the EDCA parametersbased on the legacy EDCA parameter set even in the MU EDCA mode.

Meanwhile, according to the embodiment of the present invention, the MUEDCA parameter set may be selectively used. The AP and/or STA may enableor disable the application of the MU EDCA parameter set. Hereinafter, amethod of selectively using the MU EDCA parameter set according toembodiments of the present invention will be described with reference toFIGS. 10 to 14.

FIG. 10 illustrates a method of disabling a multi-user EDCA according toan embodiment of the present invention. According to an embodiment ofthe present invention, the AP may determine whether to enable the MUEDCA. In this case, the AP may disable the MU EDCA by not including theMU EDCA parameter set element in the periodically transmitted beaconframe. In the embodiment of FIG. 10, beacon frames 522 a and 522 binclude MU EDCA parameter set element, and beacon frames 524 a and 524 bdo not include MU EDCA parameter set element.

If the MU EDCA parameter set element is not extracted from the receivedbeacon frame 524 a, the STA may switch the access category in the MUEDCA mode 60 to the legacy EDCA mode 50. In this case, the STA updatesthe EDCA parameters based on the legacy EDCA parameter set. Morespecifically, the STA may perform at least one of the followingoperations.

A-1) The STA updates the AIFSN[AC], CWmin[AC] and CWmax[AC] values ofall access categories operating in the MU EDCA mode 60 to the valuescontained in the legacy EDCA parameter set. More specifically, the STAmay update the EDCA parameters of all access categories having non-zeroMU EDCA timers to the values contained in the legacy EDCA parameter setmost recently received from the AP to which the STA is associated. Ifthe legacy EDCA parameter set has not been received from the AP to whichthe STA is associated, the STA updates the EDCA parameters of all accesscategories having non-zero MU EDCA timers to the values contained in apredetermined default EDCA parameter set. That is, the STA updates theEDCA parameters to the values contained in the legacy EDCA parameter setmost recently received from the AP to which the STA is associated, or tothe values contained in the predetermined default EDCA parameter set. Onthe other hand, no special operation is required for the access categorythat is already operating in the legacy EDCA mode 50.

A-2) The STA sets the MU EDCA timer of all access categories operatingin the MU EDCA mode 60 to zero and updates the AIFSN[AC], CWmin[AC] andCWmax[AC] values of the corresponding access category to the valuescontained in the legacy EDCA parameter set. The specific method forupdating the EDCA parameters of the STA to the values contained in thelegacy EDCA parameter set is as described in A-1). Since the MU EDCAtimer is designed to be decremented without suspension, the MU EDCAtimer may continue to decrease even after switching to the legacy EDCAmode 50 if it is not set to zero. If the MU EDCA timer reaches zerothereafter, an unnecessary management information base (MIB) update maybe performed even though the corresponding access category has alreadybeen switched to the legacy EDCA mode 50. Thus, the STA sets the MU EDCAtimer of all access categories to zero.

A-3) The STA sets the MU EDCA timer of all access categories operatingin the MU EDCA mode 60 to zero and updates the AIFSN[AC], CWmin[AC] andCWmax[AC] values of the corresponding access category to the valuecontained in the legacy EDCA parameter set. In addition, the STA newlysets the contention window based on the updated CWmin[AC] and/orCWmax[AC], and obtains the backoff timer within the set contentionwindow. As described above, according to an embodiment of the presentinvention, at least one parameter of the MU EDCA parameter set may beset to a value greater than a corresponding parameter of the legacy EDCAparameter set. In this case, when the channel access in the legacy EDCAmode 50 is performed using the contention window and the backoff timerset in the MU EDCA mode 60, channel access of the STA may be restricted.Thus, the STA resets the contention window and backoff timer of theaccess category which is switched to the legacy EDCA mode 50. Accordingto an embodiment, the STA may initialize the contention window andbackoff timer based on the legacy EDCA parameters. According to anotherembodiment, the STA may reset the contention window and backoff timerbased on the ratio between CWmin[AC] and CWmax[AC] of the legacy EDCAparameter set and CWmin[AC] and CWmax[AC] of the MU EDCA parameter set.

According to a further embodiment of the present invention, theabbreviated MU EDCA parameter set described above in FIG. 8 may be used.In this case, the STA may perform any one of the operations A-1) to A-3)when the abbreviated MU EDCA parameter set element in addition to the MUEDCA parameter set element are not extracted from the received beaconframe. If at least one of the MU EDCA parameter set element and theabbreviated MU EDCA parameter set element is extracted from the receivedbeacon frame, the STA does not perform the above operation since the APpermits the use of the MU EDCA parameters.

FIG. 11 illustrates a configuration of an operating mode indicationelement according to an embodiment of the present invention. Thenon-legacy STA may change its transmit/receive parameters and informthis change information through transmission of a separate element.According to an embodiment, the STA may change its operating modesetting using the operating mode indication (OMI) element shown in FIG.11.

The OMI information (alternatively, OMI element, OMI control field) maybe contained as a high efficiency (HE) variant of the HT control fieldof the MAC header in a frame transmitted by the non-legacy terminal. Aterminal transmitting a frame containing OMI information is defined asan OMI initiator, and a terminal receiving a frame containing OMIinformation is defined as an OMI responder. The OMI initiator that hastransmitted a frame containing OMI information can change itstransmit/receive parameters when receiving an immediate acknowledgmentfrom the OMI responder.

Referring to FIG. 11, the OMI element includes a UL-MU disable subfield.The UL-MU disable subfield indicates whether or not the correspondingSTA participates in the UL-MU transmission. More specifically, when theUL-MU disable subfield is set to zero, it indicates that the STAparticipates in the UL-MU transmission. According to an embodiment, theUL-MU transmission of the STA may be a transmission of a trigger-basedPPDU. The transmission of the trigger-based PPDU may be performed basedon a number of space-time streams of the STA in a resource unit assignedwithin the operating channel width of the STA. In this case, theoperating channel width of the STA is indicated by a channel widthsubfield of the OMI element, and the number of space-time streams of theSTA is determined within the value indicated by a transmission NSTS(i.e., Tx NSTS) subfield of the OMI element. On the other hand, when theUL-MU disable subfield is set to 1, it indicates that the UL-MUoperation of the STA is suspended. In this case, the STA does notparticipate in the UL-MU transmission until the frame containing the OMIinformation in which the UL-MU disable subfield is set to zero istransmitted.

FIG. 12 illustrates a method of controlling multi-user transmissionaccording to operating mode indication information. In the embodiment ofFIG. 12, the OMI initiator transmits a frame 610 containing OMIinformation and receives an immediate acknowledgment 620 thereto fromthe OMI responder. In this case, the UL-MU disable subfield of the OMIinformation contained in the frame 610 indicates the suspension of theUL-MU operation. That is, the UL-MU disable subfield is set to 1. Here,the OMI initiator is a non-AP STA and the OMI responder is an AP.

According to an embodiment of the present invention, the OMI responderAP considers that the OMI initiator STA that has transmitted the frame610 containing the OMI information with the UL-MU disable subfield setto 1 will not respond to any kind of trigger frame. Thus, the AP may notschedule the OMI initiator STA for UL-MU transmission. In addition, theOMI initiator STA may not be possible to transmit an immediateacknowledgment 640 in the form of UL-MU when a MAC protocol data unit(MPDU) addressed to the STA in an HE MU PPDU 630 transmitted by the APis a MAC management protocol data unit (MMPDU) or an MPDU in which an‘ACK policy’ subfield of a ‘QoS control’ subfield is set to MU ACK.Accordingly, when the OMI responder AP performs a DL-MU transmission tothe OMI initiator STA using the HE MU PPDU 630, the OMI Responder AP maynot aggregate an MPDU requesting an immediate acknowledgment 640 in theform of UL-MU to the A-MPDU transmitted to the corresponding STA. Inthis case, the MPDU requesting an immediate acknowledgment 640 in theform of UL-MU includes an action frame, a trigger frame, an MPDUcontaining an UL-MU response scheduling, an MPDU in which the ‘ACKpolicy’ subfield of the ‘QoS control’ field is set to MU ACK, and thelike.

FIG. 13 illustrates a method for disabling a multi-user EDCA accordingto another embodiment of the present invention. In addition to the casewhere the AP does not allow the use of the MU EDCA parameter set, theSTA can immediately suspend the use of the MU EDCA parameter set at aparticular point in time. The STA may suspend the use of the MU EDCAparameter set by transmitting a frame containing the OMI element withthe UL-MU disable subfield set to 1, as described above with referenceto FIG. 11.

Referring to FIG. 13, the OMI initiator STA transmits a frame 710containing OMI information with the UL-MU disable subfield set to 1 andreceives an immediate acknowledgment 720 from the OMI responder. Assuch, when the frame 710 containing OMI information in which the UL-MUdisable subfield indicates the suspension of the UL-MU operation istransmitted an immediate acknowledgment 720 from the OMI responder forthe frame 710 containing the OMI is received, the STA may switch theaccess category in the MU EDCA mode 60 to the legacy EDCA mode 50. Inthis case, the STA updates the EDCA parameters based on the legacy EDCAparameter set. More specifically, the STA may perform at least one ofthe following operations.

B-1) The STA updates the AIFSN[AC], CWmin[AC], and CWmax[AC] values ofall access categories operating in the MU EDCA mode 60 to the valuescontained in the legacy EDCA parameter set. More specifically, the STAmay update the EDCA parameters of all access categories having non-zeroMU EDCA timers to the values contained in the legacy EDCA parameter setmost recently received from the AP to which the STA is associated. Ifthe legacy EDCA parameter set has not been received from the AP to whichthe STA is associated, the STA updates the EDCA parameters of all accesscategories having non-zero MU EDCA timers to the values contained in apredetermined default EDCA parameter set. That is, the STA updates theEDCA parameters to the values contained in the legacy EDCA parameter setmost recently received from the AP to which the STA is associated, or tothe values contained in the predetermined default EDCA parameter set.

B-2) The STA sets the MU EDCA timer of all access categories operatingin the MU EDCA mode 60 to zero and updates the AIFSN[AC], CWmin[AC] andCWmax[AC] values of the corresponding access category to the valuescontained in the legacy EDCA parameter set. The specific method forupdating the EDCA parameters of the STA to the values contained in thelegacy EDCA parameter set is as described in B-1). Since the MU EDCAtimer is designed to be decremented without suspension, the MU EDCAtimer may continue to decrease even after switching to the legacy EDCAmode 50 if it is not set to zero. If the MU EDCA timer reaches zerothereafter, an unnecessary management information base (MIB) update maybe performed even though the corresponding access category has alreadybeen switched to the legacy EDCA mode 50. Thus, the STA sets the MU EDCAtimer of all access categories to zero.

B-3) The STA sets the MU EDCA timer of all access categories operatingin the MU EDCA mode 60 to zero and updates the AIFSN[AC], CWmin[AC] andCWmax[AC] values of the corresponding access category to the valuecontained in the legacy EDCA parameter set. In addition, the STA newlysets the contention window based on the updated CWmin[AC] and/orCWmax[AC], and obtains the backoff timer within the set contentionwindow. As described above, according to an embodiment of the presentinvention, at least one parameter of the MU EDCA parameter set may beset to a value larger than a corresponding parameter of the legacy EDCAparameter set. In this case, when the channel access in the legacy EDCAmode 50 is performed using the contention window and the backoff timerset in the MU EDCA mode 60, channel access of the STA may be restricted.Thus, the STA resets the contention window and backoff timer of theaccess category which is switched to the legacy EDCA mode 50. Accordingto an embodiment, the STA may initialize the contention window andbackoff timer based on the legacy EDCA parameters. According to anotherembodiment, the STA may reset the contention window and backoff timerbased on the ratio between CWmin[AC] and CWmax[AC] of the legacy EDCAparameter set and CWmin[AC] and CWmax[AC] of the MU EDCA parameter set.

FIG. 14 illustrates a method for disabling a multi-user EDCA accordingto yet another embodiment of the present invention. The STA may informthe AP that no more data is present in a particular access category toreceive UL-MU scheduling. According to an embodiment, the STA maytransmit a buffer status report through uplink to deliver the sizeinformation of the remaining data of the particular access category tothe AP.

Referring to FIG. 14, the STA may indicate the size of data remaining ina buffer of the corresponding TID, including data currently beingtransmitted, through the ‘Queue Size’ subfield of the ‘QoS Control’field of the MAC header in the trigger-based PPDUs 820 a and 820 btransmitted in response to the trigger frames 810 a and 820 b. As shownin FIG. 14(a), the STA may indicate the size of data remaining in thebuffer of each TID (i.e., TID 1, TID 0) through the ‘Queue Size’subfield of the corresponding frame. In addition, as shown in FIG.14(b), the STA may indicate the size of data remaining in the buffer ofa particular TID for which no data is transmitted through the ‘QueueSize’ subfield of a QoS Null frame.

The AP may indicate that all data transmissions are successful throughthe responses 830 a and 830 b to the PPDUs 820 a and 820 b transmittedby the STA. If the size of data indicated by the ‘Queue Size’ subfieldis the same as the size of transmitted data of the corresponding TID asin the embodiment shown in FIG. 14, no data to be transmitted isremaining in the buffer of the corresponding TID. In this case, both theAP and the STA may identify that the size of data remaining in thebuffer of the corresponding TID is 0. As in the embodiment of FIG. 14,if the buffer sizes of ‘TID 0’ and ‘TID 1’ are all 0, there is no dataremaining in a queue of ‘access category 0’. In this manner, when boththe AP and the STA identify that the buffer size of all the TIDsbelonging to a particular access category is 0 at the time the STAcompletes a UL transmission, the STA may switch the mode of thecorresponding access category from the MU EDCA mode 60 to the legacyEDCA mode 50. In this case, the STA updates the EDCA parameters of thecorresponding access category based on the legacy EDCA parameter set.More specifically, the STA may perform at least one of the followingoperations.

C-1) The STA updates the AIFSN[AC], CWmin[AC] and CWmax[AC] values ofthe corresponding access category to the values contained in the legacyEDCA parameter set. More specifically, the STA may update the EDCAparameters of the corresponding access category to the values containedin the legacy EDCA parameter set most recently received from the AP towhich the STA is associated. If the legacy EDCA parameter set has notbeen received from the AP to which the STA is associated, the STAupdates the EDCA parameters of the corresponding access category to thevalues contained in a predetermined default EDCA parameter set. That is,the STA updates the EDCA parameters to the values contained in thelegacy EDCA parameter set most recently received from the AP to whichthe STA is associated, or to the values contained in the predetermineddefault EDCA parameter set.

C-2) The STA sets the MU EDCA timer of the corresponding access categoryto zero and updates the AIFSN[AC], CWmin[AC] and CWmax[AC] values of thecorresponding access category to the values contained in the legacy EDCAparameter set. The specific method for updating the EDCA parameters ofthe STA to the values contained in the legacy EDCA parameter set is asdescribed in C-1).

C-3) The STA sets the MU EDCA timer of the corresponding access categoryoperating in the MU EDCA mode 60 to zero and updates the AIFSN[AC],CWmin[AC] and CWmax[AC] values of the corresponding access category tothe values contained in the legacy EDCA parameter set. In addition, theSTA newly sets the contention window of the corresponding accesscategory based on the updated CWmin[AC] and/or CWmax[AC], and obtainsthe backoff timer within the set contention window. The specific methodsby which the STA obtains the contention window and the backoff timer areas described in A-3) and B-3).

HE MU PPDU Configuration Method

FIGS. 15 to 17 illustrate methods of configuring an HE MU PPDU accordingto embodiments of the present invention. In the embodiments of FIGS. 15to 17, a plurality of STAs perform UL-MU transmission in response to thetrigger frame of the AP. In addition, an M-BA is received in response tothe UL-MU transmission. In this case, the M-BA is transmitted in theform of HE MU PPDU. In the embodiments of FIGS. 15 to 17, RU1, RU2, RU3,RU4, RU5 and RU6 indicate each resource unit constituting the HE MUPPDU.

FIG. 15 illustrates a configuration of an HE MU PPDU according to anembodiment of the present invention. In the non-legacy wireless LANsystem, if the trigger-based PPDU transmitted in UL-MU requests animmediate acknowledgment, the AP may transmit a block acknowledgment(BA) in the form of HE MU PPDU to a plurality of STAs. In addition, theM-BA used in the non-legacy wireless LAN system may contain ACKinformation for a plurality of STAs in a single MAC frame. Therefore, agroup addressed M-BA and an individually addressed M-BA may be mixed inone HE MU PPDU.

The HE MU PPDU may indicate, through a user information field ofHE-SIG-B, the recipient AID corresponding to each resource unit on whichtransmission is performed. In this case, a broadcast AID is insertedinto a user information field corresponding to a resource unit (i.e.,RU1) to which the group addressed M-BA is allocated, an AID of eachrecipient STA is inserted into user information fields corresponding toresource units (i.e., RU2 to RU6) to which the individually addressedM-BA is allocated. However, when a plurality of different groupaddressed M-BAs are transmitted through one HE MU PPDU, a plurality ofbroadcast AIDs corresponding to different resource units may be insertedinto the user information field of the HE-SIG-B. If an AID of a STAparticipating in the UL-MU transmission is not present in the HE-SIG-Bof the HE MU PPDU, the corresponding STA may not identify which resourceunit among the plurality of resource units corresponding to theplurality of broadcast AIDs contains its ACK information.

Thus, according to an embodiment of the present invention, when aplurality of different M-BAs are transmitted through one HE MU PPDU, arestriction that only one or less group addressed M-BA should present inthe HE MU PPDU can be applied. In addition, the AP should transmit thecorresponding M-BA on a 20 MHz channel which includes resource units inwhich the UL-MU transmission participating STAs that are the targets ofeach M-BA have transmitted the trigger-based PPDUs.

FIG. 16 illustrates a configuration of an HE MU PPDU according toanother embodiment of the present invention. According to theaforementioned embodiment, when the group addressed M-BA is transmittedthrough the particular resource unit (i.e., RU1) of the HE MU PPDU, itmay be impossible to transmit a group addressed A-MPDU through anotherresource unit. However, when an MU cascading sequence defined in thenon-legacy wireless LAN system is performed, the transmission efficiencymay be increased if a group addressed trigger frame is transmittedthrough another resource unit (e.g., RU2).

Thus, according to the embodiment of FIG. 16, a separate broadcast AIDfor the group addressed M-BA may be specified. A general broadcast AIDmay be used for a group addressed A-MPDU other than the M-BA. STAsreceiving an HE MU PPDU in the non-legacy wireless LAN system cannotreceive A-MPDU that is targeted to themselves in a plurality of resourceunits. Therefore, a STA that needs to receive an ACK from the HE MU PPDUmay receive ACK information through a resource unit (i.e., RU1) to whicha separate broadcast AID is assigned. On the other hand, a STA that isnot scheduled to receive an ACK from the HE MU PPDU may receive datathrough a resource unit corresponding to its AID, or may receive groupaddressed through trigger frame through a resource unit (i.e., RU2)corresponding to the broadcast AID.

FIG. 17 illustrates a configuration of an HE MU PPDU according to yetanother embodiment of the present invention. According to the embodimentof FIG. 17, a plurality of broadcast AIDs may be inserted into the userinformation field of the HE-SIG-B of the HE MU PPDU. In this case, anindex order of a resource unit allocation may be used to distinguish thegroup addressed M-BA and the group addressed A-MPDU other than the M-BAwithin one HE MU PPDU. The resource unit allocation field of theHE-SIG-B of the HE MU PPDU indicates division and arrangementinformation of resource units through predetermined indices. Inaddition, the user information field of the HE-SIG-B indicates the AIDvalue of each resource unit in the order according to the arrangement ofresource units indicated by the resource unit allocation field.

According to an embodiment of the present invention, when two broadcastAIDs are represented by the user information field of the HE-SIG-B ofthe HE MU PPDU, the group addressed targets may be implicitly designatedaccording to the represented order of the respective broadcast AIDs.According to an embodiment, the first represented broadcast AID mayindicate a resource unit for a group addressed M-BA, and the nextrepresented broadcast AID may indicate a resource for a group addressedA-MPDU other than the M-BA. According to another embodiment, an implicitdesignation may be performed in the reverse order. If the two broadcastAIDs are assigned to different 20 MHz channels, the implicit designationmay be performed based on the order of the channel bonding rules of thewireless LAN system.

Although the present invention is described by using the wireless LANcommunication as an example, the present invention is not limitedthereto and the present invention may be similarly applied even to othercommunication systems such as cellular communication, and the like.Further, the method, the apparatus, and the system of the presentinvention are described in association with the specific embodiments,but some or all of the components and operations of the presentinvention may be implemented by using a computer system having universalhardware architecture.

The detailed described embodiments of the present invention may beimplemented by various means. For example, the embodiments of thepresent invention may be implemented by a hardware, a firmware, asoftware, or a combination thereof.

In case of the hardware implementation, the method according to theembodiments of the present invention may be implemented by one or moreof Application Specific Integrated Circuits (ASICSs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, micro-controllers, micro-processors,and the like.

In case of the firmware implementation or the software implementation,the method according to the embodiments of the present invention may beimplemented by a module, a procedure, a function, or the like whichperforms the operations described above. Software codes may be stored ina memory and operated by a processor. The processor may be equipped withthe memory internally or externally and the memory may exchange datawith the processor by various publicly known means.

The description of the present invention is used for exemplification andthose skilled in the art will be able to understand that the presentinvention can be easily modified to other detailed forms withoutchanging the technical idea or an essential feature thereof. Thus, it isto be appreciated that the embodiments described above are intended tobe illustrative in every sense, and not restrictive. For example, eachcomponent described as a single type may be implemented to bedistributed and similarly, components described to be distributed mayalso be implemented in an associated form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

INDUSTRIAL APPLICABILITY

Various exemplary embodiments of the present invention have beendescribed with reference to an IEEE 802.11 system, but the presentinvention is not limited thereto and the present invention can beapplied to various types of mobile communication apparatus, mobilecommunication system, and the like.

1. A wireless communication terminal, the terminal comprising: acommunication unit; and a processor configured to control transmissionand reception of a wireless signal through the communication unit,wherein the processor is configured to: update enhanced distributedchannel access (EDCA) parameters for channel access, wherein the EDCAparameters are updated based on an EDCA parameter set selected from afirst EDCA parameter set and a second EDCA parameter set, and performchannel access based on the updated EDCA parameters.
 2. The wirelesscommunication terminal of claim 1, wherein the second EDCA parameter setis a multi-user (MU) EDCA parameter set, and wherein when the EDCAparameters are updated based on the MU EDCA parameter set, the processorsets an MU EDCA timer indicating a duration of performing channel accessusing parameters updated based on the MU EDCA parameter set.
 3. Thewireless communication terminal of claim 2, wherein when the terminaldoes not participate in an uplink multi-user (UL-MU) transmission, theprocessor transmits a frame containing an operating mode indication(OMI) information in which a UL-MU disable subfield indicates asuspension of a UL-MU operation, and wherein when an immediateacknowledgment for the frame containing the OMI information is receivedfrom an OMI responder, the processor sets the MU EDCA timer to zero. 4.The wireless communication terminal of claim 3, wherein when theimmediate acknowledgment for the frame containing the OMI information isreceived from the OMI responder, the processor sets MU EDCA timers ofall access categories to zero.
 5. The wireless communication terminal ofclaim 2, wherein when the MU EDCA timer reaches zero, the processorupdates the EDCA parameters based on the first EDCA parameter set mostrecently received from a base wireless communication terminal to whichthe terminal is associated.
 6. The wireless communication terminal ofclaim 2, wherein when the MU EDCA timer reaches zero, the processorupdates the EDCA parameters based on a predetermined default EDCAparameter set if the first EDCA parameter set has not been received froma base wireless communication terminal to which the terminal isassociated.
 7. The wireless communication terminal of claim 2, whereinthe MU EDCA timer is set to a value of an MU EDCA timer subfield of theMU EDCA parameter set most recently received from a base wirelesscommunication terminal to which the terminal is associated.
 8. Thewireless communication terminal of claim 1, wherein at least oneparameter of the second EDCA parameter set has a value greater than acorresponding parameter of the first EDCA parameter set.
 9. The wirelesscommunication terminal of claim 1, wherein the channel access isperformed based on a backoff procedure using a backoff timer obtainedwithin a contention window of a corresponding access category, andwherein the EDCA parameters include a contention window minimum valueand a contention window maximum value for setting the contention window.10. The wireless communication terminal of claim 1, wherein the firstEDCA parameter set and the second EDCA parameter set are received via atleast one of a beacon, a probe response, and an association responsetransmitted by a base wireless communication terminal to which theterminal is associated.
 11. A wireless communication method of awireless communication terminal, the method comprising: updatingenhanced distributed channel access (EDCA) parameters for channelaccess, wherein the EDCA parameters are updated based on an EDCAparameter set selected from a first EDCA parameter set and a second EDCAparameter set; and performing channel access based on the updated EDCAparameters.
 12. The wireless communication method of claim 11, whereinthe second EDCA parameter set is a multi-user (MU) EDCA parameter set,and wherein when the EDCA parameters are updated based on the MU EDCAparameter set, the method further comprises: setting an MU EDCA timerindicating a duration of performing channel access using parametersupdated based on the MU EDCA parameter set.
 13. The wirelesscommunication method of claim 12, wherein when the terminal does notparticipate in an uplink multi-user (UL-MU) transmission, the methodfurther comprises: transmitting a frame containing an operating modeindication (OMI) information in which a UL-MU disable subfield indicatesa suspension of a UL-MU operation, and wherein when an immediateacknowledgment for the frame containing the OMI information is receivedfrom an OMI responder, the method further comprises: setting the MU EDCAtimer to zero.
 14. The wireless communication method of claim 13,wherein when the immediate acknowledgment for the frame containing theOMI information is received from the OMI responder, the setting the MUEDCA timer to zero comprises setting MU EDCA timers of all accesscategories to zero.
 15. The wireless communication method of claim 12,wherein when the MU EDCA timer reaches zero, the updating step comprisesupdating the EDCA parameters based on the first EDCA parameter set mostrecently received from a base wireless communication terminal to whichthe terminal is associated.
 16. The wireless communication method ofclaim 12, wherein when the MU EDCA timer reaches zero, the updating stepcomprises updating the EDCA parameters based on a predetermined defaultEDCA parameter set if the first EDCA parameter set has not been receivedfrom a base wireless communication terminal to which the terminal isassociated.
 17. The wireless communication method of claim 12, whereinthe MU EDCA timer is set to a value of an MU EDCA timer subfield of theMU EDCA parameter set most recently received from a base wirelesscommunication terminal to which the terminal is associated.
 18. Thewireless communication method of claim 11, wherein at least oneparameter of the second EDCA parameter set has a value greater than acorresponding parameter of the first EDCA parameter set.
 19. Thewireless communication method of claim 11, wherein the channel access isperformed based on a backoff procedure using a backoff timer obtainedwithin a contention window of a corresponding access category, andwherein the EDCA parameters include a contention window minimum valueand a contention window maximum value for setting the contention window.20. The wireless communication method of claim 11, wherein the firstEDCA parameter set and the second EDCA parameter set are received via atleast one of a beacon, a probe response, and an association responsetransmitted by a base wireless communication terminal to which theterminal is associated.